1. Field of the Invention
The present invention relates to a diaphragm valve structure, and more specifically relates to a diaphragm valve structure which is applied to a bleed valve, a block valve or the like, which is used when a purging gas (an inactive gas, such as nitrogen gas, argon gas or the like) is continued to flow in, for example, a gas pipeline of ultrahigh purity gas for a semiconductor- or liquid crystal production line.
2. Description of the Prior Art
FIG. 9 shows one embodiment of an ultrahigh purity gas pipeline in a semiconductor- or liquid crystal production line. In exchange of a gas bomb 100 for example, in this gas pipeline, when the gas bomb 100 is removed in a state where a corrosive gas remained, the corrosive gas reacts with moisture in the air, resulting in cause to corrode the line or components or the like. In order to prevent such corrosion, when the gas bomb 100 is removed, purge of the pipeline is carried out with a purging gas. In the embodiment shown in FIG. 9, nitrogen gases 183 and 184 are used as the purging gas. In this case, the nitrogen gas 183 is used as a vacuum generating (gas removing) gas for a vacuum generator 140 and is not used for filling gas into the line. And, the above-mentioned purge is carried out by filling the line with a nitrogen gas 184 and vacuumizing from a line with the vacuum generation using the nitrogen gas 183, repeatedly. In FIG. 9, the reference numerals 111 to 117 denote stop valves, 121 and 122 needle valves, 131 to 133 check valves, 151 and 152 filters, 161 and 162 pressure gauges, and 170 pressure controller.
In a case of the pipeline shown in FIG. 9, a vacuum generator 140 is used as a vacuum generating source at the vacuum purge. This vacuum generator 140 Autilize a property (an ejector effect), that the flow velocity of fluid (a nitogen gas) is increased within a nozzle, and negative pressure is generated near the position of nozzle to suck the fluid. Even if the nitrogen gas is not caused to flow, a corrosive gas does not flow backward from a vent line 181 to the pipeline by existence of check valves 131 and 132. Nevertheless, the corrosion gas reaches the position of the vacuum generator 140. Thus, corrosion is generated in the nozzle of the vacuum generator 140 or the like, resulting in that a trouble such as occurrence of nozzle clogging is likely occurs.
When vacuum purge is not carried out, or when a stop valve 111 is closed, a stop valve 112 is opened, and the flow rate is decreased while maintaining a needle valve 121 with a desired aperture, so that a constant flow rate of nitrogen gas 183 is caused to flow into the vacuum generator 140. Thus, a constant flow rate of nitrogen gas is caused to flow into the gas pipeline so that the inflow of gas from the vent line 181 is prevented.
As another Embodiment, there is adopted a structure as shown in FIG. 10, that an air-actuated valve 181 and a needle valve 182 are connected to each other in series and a mass flow controller 185 is disposed in parallel thereto, in place of the combination of the above-mentioned stop valves 111 and 112, with the needle valve 121. According to such a structure, a gas of a constant flow rate can be caused to flow through the mass flow controller, even in a state where the air-actuated valve is closed. Further, by using a flow rate control valve such as a needle valve or the like, in place of the mass flow controller, there can be also adopted a structure by which substantially the same effects as those mentioned-above can be obtained.
Additionally, there is known a structure by which substantially the same effects as those mentioned-above can be obtained, by forming a gas flow hole for a constant flow rate, which penetrates the primary side and secondary side of a gas pipeline valve, as described in Japanese Unexamined Patent Publication (kokai) No. 6-11055, for example.
However, according to the above-mentioned conventional structure using a plurality of valves, there are problems that a number of parts are required and the cost is high.
On the other hand, in a case where a gas flow hole for a constant flow rate is formed in a gas pipeline valve, it is difficult to manufacture the gas flow hole for a constant flow rate, resulting in the cause of high costs. Further, according to such a structure, the replaceability near the valve seat is bad, and there is a possibility that the air will remain or the like.